A trendline is a straight line drawn across a series of price points to show the direction of a move. In an uptrend, the line joins a series of higher lows and sits below the price. In a downtrend, it joins lower highs and sits above the price. Traders use trendlines to judge whether a trend is still intact, to plan where a trend would be broken and to mark places where the price might pause or turn.
The line looks simple, and that is part of the problem. Two points always make a line, so a trendline can be drawn on almost any chart, and most of them will look convincing afterwards. This guide shows how to choose the points, how to test a line before you rely on it, and which errors make trendlines appear more reliable than they are.
Which points should you use?
An uptrend line joins at least two higher lows, and a downtrend line joins at least two lower highs. The line should touch the price at those points without cutting through the candles between them. A third touch that lands on the line makes it easier to justify, because the price has respected the same path more than once.
Many traders draw the line on closing prices, while others use the wicks. Choose one method and keep it for every chart you study, and note which one you used so that a later review can follow the same rule.
The angle matters. A very steep line is easy to break, because a small pause in the price crosses it. A shallow line covers a longer period and is more likely to hold, but it can also be drawn through almost any data. Some traders check the slope on a logarithmic price scale, which shows equal percentage moves as equal distances. On long-term charts this can change which lines look reasonable, so check the scale setting before you draw.
How do you project and test a line?
A trendline can be projected forward to estimate where the price would be if the trend continued at the same pace. The calculation is simple. Take two points, find the change in price per period, and extend the line. The table below uses invented prices for an uptrend. The figures are illustrative.
| Point | Day | Low | Use |
|---|---|---|---|
| First higher low | 3 | 40.0 | Anchor point for the line |
| Second higher low | 9 | 46.0 | Second point on the line |
| Slope | 1.0 per day | (46.0 − 40.0) ÷ (9 − 3) | |
| Projected line on day 12 | 12 | 49.0 | 46.0 + 3 days × 1.0 per day |
The projected value on day 12 is 49.0. If the price falls below that line by a clear margin, the uptrend described by the line is weakened, and a trader who uses it as a stop would exit. The projection is not a forecast. It is a reference for judging whether the price is still on the path the line describes.
To test a line, count how many times the price has touched it without closing through it, and note how long the line has held. A line touched several times over a long period is more meaningful than one drawn through two points last week. Check the line on a higher timeframe too. A trendline on a five-minute chart can be unrelated to the line on the daily chart, and the wider line usually matters more to the overall trend.
What breaks a trendline?
A break is usually confirmed by a close beyond the line, not by an intraday spike that returns to the line within the same session. Many traders then look for a retest, where the price returns to the broken line and fails to get back above it.
A retest that holds is more convincing than a break on a single day followed by a quick recovery.
Decide in advance how many closes beyond the line you will accept, and write the rule down before you look at the next candle. A line that is broken only by a wick, or only by a close within a small margin, may still be intact for your purposes. The purpose of the rule is to stop the decision being made after the outcome is known.
Common errors
The most common error is connecting points arbitrarily. A line drawn through a random high and a random low can always be found, so the test is whether the points are clearly significant. The second error is extending a line too far into the future, where it stops describing the price and starts describing the trader's hope.
The third is redrawing a line after each break, so that the trend always appears to be intact. A line that moves every time it fails is a record of guesses rather than a trendline.
How do you use a trendline in a trade?
A trendline is most useful as a source of levels to watch, not as a signal on its own. Traders typically look for a pullback that touches the line and holds, then enter in the direction of the trend, with a stop just beyond the line.
A close through the line is a cue to review the trade rather than a reason to act automatically.
The distance between the entry and the line sets the risk of the trade, so check whether the reward to the next obvious level justifies it before entering. A line that sits very close to the price offers a tight stop but may be broken by ordinary noise. A line far below the price allows a wide stop, and the position size should shrink to keep the loss acceptable.
Trendlines also work as a check on other tools. A moving average that sits near the same line strengthens the level, and a horizontal support zone that crosses the line is another point to watch. A line that stands alone on the chart deserves less weight than one that agrees with other evidence.
Common mistakes
Mixing wicks and closes. Choose one method, apply it to every line, and note which one you used.
Forcing a line onto a chart. If you have to squint to make the line touch the price, the trend is probably not clear enough to use.
Ignoring the scale. A line that looks right on a linear chart can look different on a log chart, especially over many years.
Checklist
- Identify at least two higher lows for an uptrend, or two lower highs for a downtrend, that are clearly significant.
- Draw the line without cutting through the candles between the anchor points.
- Check whether a third touch lands on the line, which strengthens the case for it.
- Confirm the slope is not so steep that a small pause would break it.
- Check the same line on a higher timeframe.
- Decide in advance how a break will be confirmed, such as a close beyond the line.
- Keep the original line on the chart after a break, so you can see what changed.
Key takeaways
A trendline joins at least two higher lows or two lower highs and shows the direction of a move. Its value depends on the quality of the points, the number of touches and the slope. A line can be projected forward as a reference, and a break is best confirmed by a close and a retest. Trendlines are easy to draw and easy to bend, so keep the rules fixed and keep the old lines on the chart.
This guide is for general information, not financial advice. See the disclaimer.